The Golgi complex is a key organelle where processing and sorting of newly synthesized proteins occurs. Membrane traffic from the endoplasmic reticulum (ER) to the Golgi complex and from the Golgi complex to the different final cellular destinations is believed to be mediated by carrier vesicles. Two populations of coated vesicles mediate biosynthetic membrane traffic between the different membrane-bound compartments. Clathrin-coated vesicles carry proteins to endocytic organelles and secretory granules, whilst non-clathrin-coated vesicles are involved in intra-Golgi transport and transport from the ER to the Golgi complex. Beta COP is a member of a set of protein which are believed to associate with the non-clathrin coated vesicles. Golgi-derived non-clathrin-coated vesicles are believed to act as bulk carriers, whereas clathrin-coated vesicles carry a selective cargo of membrane proteins.